1. Technical Field
The present invention relates to a power conversion apparatus in which a power semiconductor module having a plurality of semiconductor switching devices and a control circuit driving the plurality of semiconductor switching devices to be switched individually are separately isolated from each other.
2. Background Art
A power conversion apparatus which has semiconductor switching devices such as IGBTs driven to be switched to form an inverter apparatus, a chopper circuit, or the like, is used widely for various purposes. FIG. 10 is a schematic configuration diagram of an inverter apparatus which drives a three-phase AC motor (load) M. This inverter apparatus has a power semiconductor module 10 in which a plurality of (six) semiconductor switching devices (IGBTs) Q1 and Q2 to Q6 are packaged, and a control circuit 20 which drives the respective semiconductor switching devices Q1 and Q2 to Q6 to be ON/OFF while associating the semiconductor switching devices Q1 and Q2 to Q6 with one another.
Every two of the semiconductor switching devices Q1 and Q2 to Q6 are connected in series while paired with each other to form three half-bridge circuits HBs respectively. These half-bridge circuit HBs are provided in parallel to form a circuit for driving the load M. In addition, a plurality of (six) flywheel diode D1 and D2 to D6 are back-to-back connected to the semiconductor switching devices Q1 and Q2 to Q6 respectively. The half-bridge circuits drive the load M in such a manner that currents with three phases (U phase, V phase, and W phase), each 120° apart from the other two, are fed to the load M from a series connection junction of the semiconductor switching devices Q1 and Q4 forming a half-bridge circuit, a series connection junction of the semiconductor switching devices Q2 and Q5 forming a half-bridge circuit and a series connection junction of the semiconductor switching devices Q3 and Q6 forming a half-bridge circuit, respectively.
On the other hand, the control circuit 20 has a control portion 22 which includes an arithmetic unit 21 such as a CPU and which generates control signals for controlling the semiconductor switching devices Q1 and Q2 to Q6 to be ON/OFF respectively in accordance with output currents of the half-bridge circuits. Further, the control circuit 20 has a drive circuit 23 which outputs gate drive signals Vg1 and Vg2 to Vg6 for driving the semiconductor switching devices Q1 and Q2 to Q6 respectively to be ON/OFF in accordance with the control signals generated by the control portion 22.
Incidentally, information about output currents of the semiconductor switching devices Q1 and Q2 to Q6 necessary for control operation made by the control portion 22 can be obtained, for example, in such a manner that the output currents of the half-bridge circuits are detected by use of current transformers CTs respectively. However, the semiconductor switching devices Q and the flywheel diodes D have been recently provided with current detection terminals so that the current detection terminals can be used for detecting currents flowing in the semiconductor switching devices Q and the flywheel diodes D respectively to thereby obtain the control information (e.g. see PTL 1 and PTL 2, identified further on).
Incidentally, the currents flowing in the semiconductor switching devices Q and the flywheel diodes D respectively are detected by use of current detection circuits 11a and 11b to 11f connected to the current detection terminals respectively. Further, the currents which are detected by the current detection circuits 11 (11a and 11b to 11f) respectively and which flow in the semiconductor switching devices Q and the flywheel diodes D during positive and negative half-cycles respectively are combined by adders 12 (12a and 12b to 12c) as shown in FIG. 10 to thereby obtain one-cycle's currents which flow through the half-bridge circuits respectively.
Incidentally, for example, each of the output currents of the half-bridge circuits detected by use of the current transformers CTs or the like has a sine-wave current waveform as shown in FIG. 11(a). The output current with only one phase is illustrated here. However, for example, each of the currents detected through the current detection terminals of the semiconductor switching devices Q and the flywheel diodes D has a discrete-pulsed sine-wave current waveform synchronized with a switching operation period of the semiconductor switching device Q as shown in FIG. 11(b).